Thickness measurement plays an important role in the monitoring of pipeline corrosion damage. However, the requirement for prior knowledge of the shear wave velocity in the pipeline material for popular ultrasonic thi...Thickness measurement plays an important role in the monitoring of pipeline corrosion damage. However, the requirement for prior knowledge of the shear wave velocity in the pipeline material for popular ultrasonic thickness measurement limits its widespread application. This paper proposes a method that utilizes cylindrical shear horizontal(SH) guided waves to estimate pipeline thickness without prior knowledge of shear wave velocity. The inversion formulas are derived from the dispersion of higher-order modes with the high-frequency approximation. The waveform of the example problems is simulated using the real-axis integral method. The data points on the dispersion curves are processed in the frequency domain using the wave-number method. These extracted data are then substituted into the derived formulas. The results verify that employing higher-order SH guided waves for the evaluation of thickness and shear wave velocity yields less than1% error. This method can be applied to both metallic and non-metallic pipelines, thus opening new possibilities for health monitoring of pipeline structures.展开更多
Acoustic radiation force(ARF), as an important particle manipulation method, has been extensively studied in recent years. With the introduction of the concept of “acoustic tweezers”, negative acoustic radiation has...Acoustic radiation force(ARF), as an important particle manipulation method, has been extensively studied in recent years. With the introduction of the concept of “acoustic tweezers”, negative acoustic radiation has become a research hotspot. In this paper, a scheme of realizing negative ARF based on the multiple-layered spherical structure design is proposed. The specific structure and design idea are presented. Detailed theoretical calculation analysis is carried out.Numerical simulations have been performed to verify the correctness of this prediction. The conjecture that the suppression of backscattering can achieve negative ARF is verified concretely, which greatly expands the application prospect and design ideas of the ARF. This work has laid a theoretical foundation for realizing precise control of the structure.展开更多
The shallow-water temperature profile is typically parameterized using a few empirical orthogonal function(EOF)coefficients.However,when the experimental area is poorly known or highly variable,the adaptability of the...The shallow-water temperature profile is typically parameterized using a few empirical orthogonal function(EOF)coefficients.However,when the experimental area is poorly known or highly variable,the adaptability of the EOFs will be significantly reduced.In this study,a new set of basis functions,generated by combining the internal-wave eigenmodes with the average temperature gradient,is developed for characterizing the temperature perturbations.Temperature profiles recorded by a thermistor chain in the South China Sea in 2015 are processed and analyzed.Compared to the EOFs,the new set of basis functions has higher reconstruction accuracy and adaptability;it is also more stable in ocean regions that have internal waves.展开更多
Modeling of a drill-string acoustic channel has been an important topic in downhole telemetry for a long time.The propagation of drill-string guided waves in the borehole contains excitation,attenuation,and mode conve...Modeling of a drill-string acoustic channel has been an important topic in downhole telemetry for a long time.The propagation of drill-string guided waves in the borehole contains excitation,attenuation,and mode conversion issues that have not been considered by existing modeling methods.In this article,we formulate a hybrid modeling method to investigate the response characteristics of a fundamental-mode drill-string wave in various borehole environments.This hybrid method provides channel functions,including transmitting and receiving deployments,periodicity of the structure,and formation property changes.The essential physics of the drill-string wave propagation is captured with a one-dimensional model.The analytical solutions of the wavefield in multilayered cylindrical structures are introduced into a propagation matrix to express drill-string-wave interactions with the borehole environments.The effectiveness of the proposed method is confirmed through comparison with the finite-difference method.In addition,by designing numerical models,we investigate the conversion effect of the drill-string wave at the tool joint.We demonstrate that the conversion intensity of the drill-string wave is positively correlated not only with the cross-sectional area of the tool joint but also with the wave impedance of the outer formation.Hard formation outside the borehole reduces the energy leakage while intensifying the conversion of drill-string waves to Stoneley waves,and the opposite is true for the drill string in an infinite fluid.The converted Stoneley waves interfere with the drill-string waves,resulting in variations of bandgap distribution,which challenges the reliability of the data transmission.展开更多
We demonstrate a method to realize unidirectional negative refraction in an acoustic parity-time(P T)-symmetric system, which is composed of a pair of metasurfaces sandwiching an air gap. The pair of metasurfaces poss...We demonstrate a method to realize unidirectional negative refraction in an acoustic parity-time(P T)-symmetric system, which is composed of a pair of metasurfaces sandwiching an air gap. The pair of metasurfaces possesses loss and gain modulations. The unidirectional negative refraction, which is strictly limited to the case of incident wave imposing on the loss end of the metasurface, is demonstrated at the exception point(EP) in this P T-symmetric system, while the incidence from the other side leads to strong reflection. Based on rigorous calculations, we explicitly show the underlying mechanism of this model to achieve unidirectional wave scatterings around the EP in the parametric space. In addition, the perfect imaging of a point source in the three-dimensional space, as a signature of negative refraction, is simulated to provide a verification of our work. We envision that this work may sharpen the understanding of P T-symmetric structures and inspire more acoustic functional devices.展开更多
Western Subarctic Gyre(WSG),which possesses distinctive differences in oceanographic and biogeochemical processes,is situated in the northwest subarctic Pacific.The WSG is characterized by high nutrient and low chloro...Western Subarctic Gyre(WSG),which possesses distinctive differences in oceanographic and biogeochemical processes,is situated in the northwest subarctic Pacific.The WSG is characterized by high nutrient and low chlorophyll.We carried out a field investigation in this area in summer 2020 and performed microscopic observation,cytometric counting,and RuBisCO large subunit(rbc L)gene analysis to understand the community structure and spatial distribution of chromophytic phytoplankton better.Microscopic method revealed that total phytoplankton(>10μm,including Bacillariophyta,Dinoflagellata,Ochrophyta,and Chlorophyta)abundances ranged(0.6×10^(3))-(167.4×10^(3))cells/L with an increasing trend from south to north.Dinoflagellates and Pennatae diatoms dominated the phytoplankton assemblages in the southern and northern stations,respectively.Major chromophytic phytoplankton groups derived from rbc L genes included Haptophyta,Ochrophyta,Bacillariophyta,as well as rarely occurring groups,such as Xanthophyta,Cyanobacteria,Dinoflagellata,Rhodophyta,and Cryptophyta.At the phylum level,Haptophyta was the most abundant phylum,accounting for approximately 30.80%of the total obtained operational taxonomic units in all samples.Ochrophyta and Bacillariophyta were the second and third most abundant phylum,and their relative abundance was 20.26% and 19.60%,respectively.Further,redundancy analysis showed that high proportion of diatoms(e.g.,microscopic and rbc L methods)was positively correlated with nutrients(e.g.,dissolved inorganic nitrogen(DIN),dissolved inorganic phosphorous,and dissolved silicate(DSi))and negatively correlated with temperature and salinity.The proportion of Ochrophyta,Rhodophyta,and Cyanobateria identified by rbc L genes was positively correlated with salinity and temperature and showed negative correlation to nutrients.This work is the first molecular study of phytoplankton accomplished in the WSG,and our results show some discrepancies between morphological observation and rbc L gene sequences,which highlight the necessity of combining the microscopic and molecular methods to reveal the diversity of phytoplankton in marine environment.展开更多
The acoustic properties of seafloor sediment are essential parameters in the exploration of marine resources,ocean scientific research and ocean engineering.Seafloor sediment samples were collected at the southern U-b...The acoustic properties of seafloor sediment are essential parameters in the exploration of marine resources,ocean scientific research and ocean engineering.Seafloor sediment samples were collected at the southern U-boundary of the South China Sea(SCS),and the acoustic and physical properties were measured in the laboratory.The correlation between physical and sound speed ratio(SSR)was discussed,and SSR-physical property empirical regressions in the Sunda Shelf were established for the first time.Compared with the northern continental shelf of SCS,the Sunda Shelf are mainly silty and sand sediment,and the SSR ranges from 0.9949 to 1.0944,which has higher SSR than the northern continental shelf,implies that the Sunda Shelf is a high SSR area.Since the same kind of sediment has different physical properties,the single physical parameter of sediment cannot fully represent the acoustic properties of sediment,therefore,the multiple parameter prediction model should develop in the future to improve the prediction precision.展开更多
The estimation of sparse underwater acoustic(UWA)channels can be regarded as an inference problem involving hidden variables within the Bayesian framework.While the classical sparse Bayesian learning(SBL),derived thro...The estimation of sparse underwater acoustic(UWA)channels can be regarded as an inference problem involving hidden variables within the Bayesian framework.While the classical sparse Bayesian learning(SBL),derived through the expectation maximization(EM)algorithm,has been widely employed for UWA channel estimation,it still differs from the real posterior expectation of channels.In this paper,we propose an approach that combines variational inference(VI)and Markov chain Monte Carlo(MCMC)methods to provide a more accurate posterior estimation.Specifically,the SBL is first re-derived with VI,allowing us to replace the posterior distribution of the hidden variables with a variational distribution.Then,we determine the full conditional probability distribution for each variable in the variational distribution and then iteratively perform random Gibbs sampling in MCMC to converge the Markov chain.The results of simulation and experiment indicate that our estimation method achieves lower mean square error and bit error rate compared to the classic SBL approach.Additionally,it demonstrates an acceptable convergence speed.展开更多
Underwater acoustic applications depend critically on the prediction of sound propagation, which can be significantly affected by a rough surface, especially in shallow water. This paper aims to investigate how random...Underwater acoustic applications depend critically on the prediction of sound propagation, which can be significantly affected by a rough surface, especially in shallow water. This paper aims to investigate how randomly fluctuating surface influences transmission loss(TL) in shallow water. The one-dimension wind-wave spectrum, Monterey–Miami parabolic equation(MMPE) model, Monte Carlo method, and parallel computing technology are combined to investigate the effects of different sea states on sound propagation. It is shown that TL distribution properties are related to the wind speed,frequency, range, and sound speed profile. In a homogenous waveguide, with wind speed increasing, the TLs are greater and more dispersive. For a negative thermocline waveguide, when the source is above the thermocline and the receiver is below that, the effects of the rough surface are the same and more significant. When the source and receiver are both below the thermocline, the TL distributions are nearly the same for different wind speeds. The mechanism of the different TL distribution properties in the thermocline environment is explained by using ray theory. In conclusion, the statistical characteristics of TL are affected by the relative roughness of the surface, the interaction strength of the sound field with the surface, and the changes of propagating angle due to refraction.展开更多
Using deep convolutional neural networks as primary learners and a deep neural network as meta-learner, source ranging is solved as a regression problem with the ensemble learning method. Simulated acoustic data from ...Using deep convolutional neural networks as primary learners and a deep neural network as meta-learner, source ranging is solved as a regression problem with the ensemble learning method. Simulated acoustic data from the acoustic propagation model are used as the training data. Real data from an experiment in the South China Sea are used as the test data to demonstrate the performance. The results indicate that in the direct zone of deep water, signals received by a very deep receiver can be used to estimate the range of underwater sound source.Within 30 km, the mean absolute error of the range predictions is 1.0 km and the mean absolute percentage error is 7.9%.展开更多
Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss (TL) data in ...Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss (TL) data in the shadow zone of deep water. We propose a multiple-step fill inversion method to invert sound speed, density and attenuation in deep water. Based on a uniform liquid hMf-space bottom model, sound speed of the bottom is inverted by using the long range TL at low frequency obtained in an acoustic propagation experiment conducted in the South China Sea (SCS) in summer 2014. Meanwhile, bottom density is estimated combining with the Hamilton sediment empirical relationship. Attenuation coefficients at different frequencies are then estimated from the TL data in the shadow zones by using the known sound speed and density as a constraint condition. The nonlinear relationship between attenuation coefficient and frequency is given in the end. Tile inverted bottom parameters can be used to forecast the transmission loss in the deep water area of SCS very we//.展开更多
The estimation of ocean sound speed profiles(SSPs)requires the inversion of an acoustic field using limited observations.Such inverse problems are underdetermined,and require regularization to ensure physically realis...The estimation of ocean sound speed profiles(SSPs)requires the inversion of an acoustic field using limited observations.Such inverse problems are underdetermined,and require regularization to ensure physically realistic solutions.The empirical orthonormal function(EOF)is capable of a very large compression of the data set.In this paper,the non-linear response of the sound pressure to SSP is linearized using a first order Taylor expansion,and the pressure is expanded in a sparse domain using EOFs.Since the parameters of the inverse model are sparse,compressive sensing(CS)can help solve such underdetermined problems accurately,efficiently,and with enhanced resolution.Here,the orthogonal matching pursuit(OMP)is used to estimate range-independent acoustic SSPs using the simulated acoustic field.The superior resolution of OMP is demonstrated with the SSP data from the South China Sea experiment.By shortening the duration of the training set,the temporal correlation between EOF and test sets is enhanced,and the accuracy of sound velocity inversion is improved.The SSP estimation error versus depth is calculated,and the 99%confidence interval of error is within±0.6 m/s.The 82%of mean absolute error(MAE)is less than 1 m/s.It is shown that SSPs can be well estimated using OMP.展开更多
The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the ...The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterbome modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.展开更多
Sound multipath propagation is very important for target localization and identification in different acoustical zones of deep water. In order to distinguish the multipath characteristics in deep water, the Northwest ...Sound multipath propagation is very important for target localization and identification in different acoustical zones of deep water. In order to distinguish the multipath characteristics in deep water, the Northwest Pacific Acoustic Experiment was conducted in 2015. A low-frequency horizontal line array towed at the depth of around 150 m on a receiving ship was used to receive the noise radiated by the source ship. During this experiment, a beating-splitting phenomenon in the direct zone was observed through conventional beamforming of the horizontal line array within the frequency band 160 Hz- 360 Hz. In this paper, this phenomenon is explained based on ray theory. In principle, the received signal in the direct zone of deep water arrives from two general paths including a direct one and bottom bounced one, which vary considerably in arrival angles. The split bearings correspond to the contributions of these two paths. The beating-splitting phenomenon is demonstrated by numerical simulations of the bearing-time records and experimental results, and they are well consistent with each other. Then a near-surface source ranging approach based on the arrival angles of direct path and bottom bounced path in the direct zone is presented as an application of bearing splitting and is verified by experimental results. Finally, the applicability of the proposed ranging approach for an underwater source within several hundred meters in depth in the direct zone is also analyzed and demonstrated by simulations.展开更多
Based on the exact solutions for the second-harmonic generations of the fundamental longitudinal and transverse waves propagating normally through a thin elastic layer between two solids, the approximate representatio...Based on the exact solutions for the second-harmonic generations of the fundamental longitudinal and transverse waves propagating normally through a thin elastic layer between two solids, the approximate representations termed as 'nonlinear spring models' relating the stresses and displacements on both sides of the interface are rigorously developed by asymptotic expansions of the wave fields for an elastic layer in the limit of small thickness to wavelength ratio. The applicability for the so-called nonlinear spring models is numerically analyzed by comparison with exact solutions for the second harmonic wave reflections. The present nonlinear spring models lay a theoretical foundation to evaluate the interracial properties by nonlinear acoustic waves.展开更多
Ultrasonic inspection of austenitic steel weld is a great challenge due to skewed and distorted beam in such a highly anisotropic and inhomogeneous material. To improve the ultrasonic measurement in this situation, it...Ultrasonic inspection of austenitic steel weld is a great challenge due to skewed and distorted beam in such a highly anisotropic and inhomogeneous material. To improve the ultrasonic measurement in this situation, it is essential to have an in-depth understanding of ultrasound characteristics in austenitic steel weld. To meet such a need, in the present study we propose a method which combines the weld model, Dijkstra’s path-finding algorithm and Gaussian beam equivalent point source model to calculate the acoustic fields from ultrasonic phased array in such a weld. With this method, the acoustic field in a steel-austenitic weld-steel three-layered structure for a linear phase array transducer is calculated and the propagation characteristics of ultrasound in weld are studied. The research results show that the method proposed here is capable of calculating the acoustic field in austenitic weld. Additionally, beam steering and focusing can be still realized in the austenitic steel weld and the beam distortion is more severe in the middle of weld than at other positions.展开更多
The phase relation of harmonics in high-intensity focused ultrasound is investigated numerically and experimen- tally. The nonlinear Westervelt equation is solved to model nonlinear focused sound field by using the fi...The phase relation of harmonics in high-intensity focused ultrasound is investigated numerically and experimen- tally. The nonlinear Westervelt equation is solved to model nonlinear focused sound field by using the finite difference time domain method. Experimental waveforms are measured by a robust needle hydrophone. Then the relative phase quantity is introduced and obtained by using the zero-phase filter. The results show that the nth harmonic relative phase quantity is approximately (n - 1) π/3 at geometric center and increases along the axial direction. Moreover, the relative phase quantity decreases with the increase of source amplitude. This phase relation gives an explanation of some nonlinear phenomena such as the discrepancy of positive and negative pressure.展开更多
Theoretical and numerical study on the coupling acoustic field of the plane p-wave to a cased borehole is carried out. The medium outside the cased borehole is modeled as the porous medium. The scattering field charac...Theoretical and numerical study on the coupling acoustic field of the plane p-wave to a cased borehole is carried out. The medium outside the cased borehole is modeled as the porous medium. The scattering field characteristics in the cased borehole are investigated when a plane fast p-wave is incident in tilt to the cased borehole from the porous medium. The scattering fields inside and outside the cased borehole are analyzed and deduced by Biot's theory under the boundary conditions on each interface, and they are numerically studied. It is found that the scattering field has strong resonant characteristics and there exists a series of resonant frequencies and peaks. The effects of the frequency, radii of each interface, incident angle, porosity, and other parameters on the resonant acoustic field have been investigated in detail in the fast and slow formations respectively. The resonant characteristics of the scattering field are also analyzed from the physical sense.展开更多
Ocean noise recorded during a typhoon can be used to monitor the typhoon and investigate the mechanism of the wind- generated noise. An analytical expression for the typhoon-generated noise intensity is derived as a f...Ocean noise recorded during a typhoon can be used to monitor the typhoon and investigate the mechanism of the wind- generated noise. An analytical expression for the typhoon-generated noise intensity is derived as a function of wind speed. A "bi-peak" structure was observed in an experiment during which typhoon-generated noise was recorded. Wind speed dependence and frequency dependence were also observed in the frequency range of 100 Hz-1000 Hz. The model/data comparison shows that results of the present model of 500 Hz and 1000 Hz are in reasonable agreement with the exper- imental data, and the typhoon-generated noise intensity has a dependence on frequency and a power-law dependence on wind speed.展开更多
The horizontal-longitudinal correlations of the acoustic field in deep water are investigated based on the experi- mental data obtained in the South China Sea. It is shown that the horizontal-longitudinal correlation ...The horizontal-longitudinal correlations of the acoustic field in deep water are investigated based on the experi- mental data obtained in the South China Sea. It is shown that the horizontal-longitudinal correlation coefficients in the convergence zone are high, and the correlation length is consistent with the convergence zone width, which depends on the receiver depth and range. The horizontal-longitudinal correlation coefficients in the convergence zone also have a division structure for the deeper receiver. The signals from the second part of the convergence zone are still correlated with the reference signal in the first part. The horizontal-longitudinal correlation coeffi- cients in the shadow zone are lower than that in the convergence zone, and the correlation length in the shadow zone is also much shorter than that in the convergence zone. The numerical simulation results by using the normal modes theory are qualitatively consistent with the experimental results.展开更多
基金Project supported by the Natural Science Foundation of Jilin Province of China(Grant Nos.20240402081GH and 20220101012JC)the National Natural Science Foundation of China(Grant No.42074139)the State Key Laboratory of Acoustics,Chinese Academy of Sciences(Grant No.SKLA202308)。
文摘Thickness measurement plays an important role in the monitoring of pipeline corrosion damage. However, the requirement for prior knowledge of the shear wave velocity in the pipeline material for popular ultrasonic thickness measurement limits its widespread application. This paper proposes a method that utilizes cylindrical shear horizontal(SH) guided waves to estimate pipeline thickness without prior knowledge of shear wave velocity. The inversion formulas are derived from the dispersion of higher-order modes with the high-frequency approximation. The waveform of the example problems is simulated using the real-axis integral method. The data points on the dispersion curves are processed in the frequency domain using the wave-number method. These extracted data are then substituted into the derived formulas. The results verify that employing higher-order SH guided waves for the evaluation of thickness and shear wave velocity yields less than1% error. This method can be applied to both metallic and non-metallic pipelines, thus opening new possibilities for health monitoring of pipeline structures.
基金Project supported by the National Key Research and Development Program of China (Grant No.2020YFA0211400)the State Key Program of the National Natural Science Foundation of China (Grant No.11834008)+3 种基金the National Natural Science Foundation of China (Grant Nos.12174192 and 12204119)the Fund from the State Key Laboratory of Acoustics,Chinese Academy of Sciences (Grant No.SKLA202210)the Fund from the Key Laboratory of Underwater Acoustic Environment,Chinese Academy of Sciences (Grant No.SSHJ-KFKT-1701)the Science and Technology Foundation of Guizhou Province,China (Grant No.ZK[2023]249)。
文摘Acoustic radiation force(ARF), as an important particle manipulation method, has been extensively studied in recent years. With the introduction of the concept of “acoustic tweezers”, negative acoustic radiation has become a research hotspot. In this paper, a scheme of realizing negative ARF based on the multiple-layered spherical structure design is proposed. The specific structure and design idea are presented. Detailed theoretical calculation analysis is carried out.Numerical simulations have been performed to verify the correctness of this prediction. The conjecture that the suppression of backscattering can achieve negative ARF is verified concretely, which greatly expands the application prospect and design ideas of the ARF. This work has laid a theoretical foundation for realizing precise control of the structure.
基金The Natural Science Foundation of Shandong Province of China under contract Nos ZR2022MA051 and ZR2020MA090the Fund of China Postdoctoral Science Foundation under contract No.2020M670891+1 种基金the Shandong University of Science and Technology Research Fund under contract No.2019TDJH103the Talent Introduction Plan for Youth Innovation Team in Universities of Shandong Province(Innovation Team of Satellite Positioning and Navigation).
文摘The shallow-water temperature profile is typically parameterized using a few empirical orthogonal function(EOF)coefficients.However,when the experimental area is poorly known or highly variable,the adaptability of the EOFs will be significantly reduced.In this study,a new set of basis functions,generated by combining the internal-wave eigenmodes with the average temperature gradient,is developed for characterizing the temperature perturbations.Temperature profiles recorded by a thermistor chain in the South China Sea in 2015 are processed and analyzed.Compared to the EOFs,the new set of basis functions has higher reconstruction accuracy and adaptability;it is also more stable in ocean regions that have internal waves.
基金the National Natural Science Foundation of China(Grant Nos.11734017 and 12174421)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(Grant Nos.YJKYYQ20200072 and GJJSTD20210008).
文摘Modeling of a drill-string acoustic channel has been an important topic in downhole telemetry for a long time.The propagation of drill-string guided waves in the borehole contains excitation,attenuation,and mode conversion issues that have not been considered by existing modeling methods.In this article,we formulate a hybrid modeling method to investigate the response characteristics of a fundamental-mode drill-string wave in various borehole environments.This hybrid method provides channel functions,including transmitting and receiving deployments,periodicity of the structure,and formation property changes.The essential physics of the drill-string wave propagation is captured with a one-dimensional model.The analytical solutions of the wavefield in multilayered cylindrical structures are introduced into a propagation matrix to express drill-string-wave interactions with the borehole environments.The effectiveness of the proposed method is confirmed through comparison with the finite-difference method.In addition,by designing numerical models,we investigate the conversion effect of the drill-string wave at the tool joint.We demonstrate that the conversion intensity of the drill-string wave is positively correlated not only with the cross-sectional area of the tool joint but also with the wave impedance of the outer formation.Hard formation outside the borehole reduces the energy leakage while intensifying the conversion of drill-string waves to Stoneley waves,and the opposite is true for the drill string in an infinite fluid.The converted Stoneley waves interfere with the drill-string waves,resulting in variations of bandgap distribution,which challenges the reliability of the data transmission.
基金supported by the National Key R&D Program of China (Grant Nos. 2022YFA1404400 and 2022YFA1404403)the National Natural Science Foundation of China (Grant No. 92263208)+3 种基金the Natural Science Foundation of Jiangsu Province (Grant No. BK20210541)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No. 21KJB140003)the Fundamental Research Funds for the Central Universitiesthe Open Fund of State Key Laboratory of Acoustics (Grant No. SKLA202313)。
文摘We demonstrate a method to realize unidirectional negative refraction in an acoustic parity-time(P T)-symmetric system, which is composed of a pair of metasurfaces sandwiching an air gap. The pair of metasurfaces possesses loss and gain modulations. The unidirectional negative refraction, which is strictly limited to the case of incident wave imposing on the loss end of the metasurface, is demonstrated at the exception point(EP) in this P T-symmetric system, while the incidence from the other side leads to strong reflection. Based on rigorous calculations, we explicitly show the underlying mechanism of this model to achieve unidirectional wave scatterings around the EP in the parametric space. In addition, the perfect imaging of a point source in the three-dimensional space, as a signature of negative refraction, is simulated to provide a verification of our work. We envision that this work may sharpen the understanding of P T-symmetric structures and inspire more acoustic functional devices.
基金Supported by the National Key Research and Development Program of China(No.2019YFD0901401)the National Natural Science Foundation of China(Nos.42176206,81900630)+2 种基金the Natural Science Foundation of Shandong Province(No.ZR2021MD071)the“One Hundred Talents”Project of Guangxi(No.6020303891251)the Outstanding Youth Project of Yunnan Provincial Department of Science and Technology(No.2019F1019)。
文摘Western Subarctic Gyre(WSG),which possesses distinctive differences in oceanographic and biogeochemical processes,is situated in the northwest subarctic Pacific.The WSG is characterized by high nutrient and low chlorophyll.We carried out a field investigation in this area in summer 2020 and performed microscopic observation,cytometric counting,and RuBisCO large subunit(rbc L)gene analysis to understand the community structure and spatial distribution of chromophytic phytoplankton better.Microscopic method revealed that total phytoplankton(>10μm,including Bacillariophyta,Dinoflagellata,Ochrophyta,and Chlorophyta)abundances ranged(0.6×10^(3))-(167.4×10^(3))cells/L with an increasing trend from south to north.Dinoflagellates and Pennatae diatoms dominated the phytoplankton assemblages in the southern and northern stations,respectively.Major chromophytic phytoplankton groups derived from rbc L genes included Haptophyta,Ochrophyta,Bacillariophyta,as well as rarely occurring groups,such as Xanthophyta,Cyanobacteria,Dinoflagellata,Rhodophyta,and Cryptophyta.At the phylum level,Haptophyta was the most abundant phylum,accounting for approximately 30.80%of the total obtained operational taxonomic units in all samples.Ochrophyta and Bacillariophyta were the second and third most abundant phylum,and their relative abundance was 20.26% and 19.60%,respectively.Further,redundancy analysis showed that high proportion of diatoms(e.g.,microscopic and rbc L methods)was positively correlated with nutrients(e.g.,dissolved inorganic nitrogen(DIN),dissolved inorganic phosphorous,and dissolved silicate(DSi))and negatively correlated with temperature and salinity.The proportion of Ochrophyta,Rhodophyta,and Cyanobateria identified by rbc L genes was positively correlated with salinity and temperature and showed negative correlation to nutrients.This work is the first molecular study of phytoplankton accomplished in the WSG,and our results show some discrepancies between morphological observation and rbc L gene sequences,which highlight the necessity of combining the microscopic and molecular methods to reveal the diversity of phytoplankton in marine environment.
基金Supported by the Guangdong Special Support Key Team Program(No.2019BT02H594)the National Key R&D Program of China(No.2021YFF0501202)+5 种基金the Youth Innovation Promotion Association CASthe National Natural Science Foundation of China(Nos.41706045,42176191,41773039,U22A2012)the Rising Star Foundation of the Integrated Research Center for Islands and Reefs Sciences,CAS(No.ZDRW-XH-2021-2-03)the CAS Key Laboratory of Science and Technology on Operational Oceanography Open Project Funding(No.OOST2021-01)the Guangdong Natural Science Foundation(No.2017A030313237)the State Key Laboratory of Acoustics,Chinese Academy of Sciences(Nos.SKLA202007,SKLA202106)。
文摘The acoustic properties of seafloor sediment are essential parameters in the exploration of marine resources,ocean scientific research and ocean engineering.Seafloor sediment samples were collected at the southern U-boundary of the South China Sea(SCS),and the acoustic and physical properties were measured in the laboratory.The correlation between physical and sound speed ratio(SSR)was discussed,and SSR-physical property empirical regressions in the Sunda Shelf were established for the first time.Compared with the northern continental shelf of SCS,the Sunda Shelf are mainly silty and sand sediment,and the SSR ranges from 0.9949 to 1.0944,which has higher SSR than the northern continental shelf,implies that the Sunda Shelf is a high SSR area.Since the same kind of sediment has different physical properties,the single physical parameter of sediment cannot fully represent the acoustic properties of sediment,therefore,the multiple parameter prediction model should develop in the future to improve the prediction precision.
基金funded by the Excellent Youth Science Fund of Heilongjiang Province(Grant No.YQ2022F001).
文摘The estimation of sparse underwater acoustic(UWA)channels can be regarded as an inference problem involving hidden variables within the Bayesian framework.While the classical sparse Bayesian learning(SBL),derived through the expectation maximization(EM)algorithm,has been widely employed for UWA channel estimation,it still differs from the real posterior expectation of channels.In this paper,we propose an approach that combines variational inference(VI)and Markov chain Monte Carlo(MCMC)methods to provide a more accurate posterior estimation.Specifically,the SBL is first re-derived with VI,allowing us to replace the posterior distribution of the hidden variables with a variational distribution.Then,we determine the full conditional probability distribution for each variable in the variational distribution and then iteratively perform random Gibbs sampling in MCMC to converge the Markov chain.The results of simulation and experiment indicate that our estimation method achieves lower mean square error and bit error rate compared to the classic SBL approach.Additionally,it demonstrates an acceptable convergence speed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11434012,11874061,and 41561144006)
文摘Underwater acoustic applications depend critically on the prediction of sound propagation, which can be significantly affected by a rough surface, especially in shallow water. This paper aims to investigate how randomly fluctuating surface influences transmission loss(TL) in shallow water. The one-dimension wind-wave spectrum, Monterey–Miami parabolic equation(MMPE) model, Monte Carlo method, and parallel computing technology are combined to investigate the effects of different sea states on sound propagation. It is shown that TL distribution properties are related to the wind speed,frequency, range, and sound speed profile. In a homogenous waveguide, with wind speed increasing, the TLs are greater and more dispersive. For a negative thermocline waveguide, when the source is above the thermocline and the receiver is below that, the effects of the rough surface are the same and more significant. When the source and receiver are both below the thermocline, the TL distributions are nearly the same for different wind speeds. The mechanism of the different TL distribution properties in the thermocline environment is explained by using ray theory. In conclusion, the statistical characteristics of TL are affected by the relative roughness of the surface, the interaction strength of the sound field with the surface, and the changes of propagating angle due to refraction.
基金the National Natural Science Foundation of China under Grant Nos 11434012 and 11874061
文摘Using deep convolutional neural networks as primary learners and a deep neural network as meta-learner, source ranging is solved as a regression problem with the ensemble learning method. Simulated acoustic data from the acoustic propagation model are used as the training data. Real data from an experiment in the South China Sea are used as the test data to demonstrate the performance. The results indicate that in the direct zone of deep water, signals received by a very deep receiver can be used to estimate the range of underwater sound source.Within 30 km, the mean absolute error of the range predictions is 1.0 km and the mean absolute percentage error is 7.9%.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11434012,41561144006,11174312 and 11404366
文摘Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss (TL) data in the shadow zone of deep water. We propose a multiple-step fill inversion method to invert sound speed, density and attenuation in deep water. Based on a uniform liquid hMf-space bottom model, sound speed of the bottom is inverted by using the long range TL at low frequency obtained in an acoustic propagation experiment conducted in the South China Sea (SCS) in summer 2014. Meanwhile, bottom density is estimated combining with the Hamilton sediment empirical relationship. Attenuation coefficients at different frequencies are then estimated from the TL data in the shadow zones by using the known sound speed and density as a constraint condition. The nonlinear relationship between attenuation coefficient and frequency is given in the end. Tile inverted bottom parameters can be used to forecast the transmission loss in the deep water area of SCS very we//.
基金The National Natural Science Foundation of China under contract No.11704225the Shandong Provincial Natural Science Foundation under contract No.ZR2016AQ23+3 种基金the State Key Laboratory of Acoustics,Chinese Academy of Sciences under contract No.SKLA201902the National Key Research and Development Program of China contract No.2018YFC1405900the SDUST Research Fund under contract No.2019TDJH103the Talent Introduction Plan for Youth Innovation Team in Universities of Shandong Province(Innovation Team of Satellite Positioning and Navigation)
文摘The estimation of ocean sound speed profiles(SSPs)requires the inversion of an acoustic field using limited observations.Such inverse problems are underdetermined,and require regularization to ensure physically realistic solutions.The empirical orthonormal function(EOF)is capable of a very large compression of the data set.In this paper,the non-linear response of the sound pressure to SSP is linearized using a first order Taylor expansion,and the pressure is expanded in a sparse domain using EOFs.Since the parameters of the inverse model are sparse,compressive sensing(CS)can help solve such underdetermined problems accurately,efficiently,and with enhanced resolution.Here,the orthogonal matching pursuit(OMP)is used to estimate range-independent acoustic SSPs using the simulated acoustic field.The superior resolution of OMP is demonstrated with the SSP data from the South China Sea experiment.By shortening the duration of the training set,the temporal correlation between EOF and test sets is enhanced,and the accuracy of sound velocity inversion is improved.The SSP estimation error versus depth is calculated,and the 99%confidence interval of error is within±0.6 m/s.The 82%of mean absolute error(MAE)is less than 1 m/s.It is shown that SSPs can be well estimated using OMP.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11434012 and 41561144006)
文摘The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterbome modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.
基金Project supported by the Program of One Hundred Talented People of the Chinese Academy of SciencesNational Natural Science Foundation of China(Grant Nos.11434012 and 41561144006)
文摘Sound multipath propagation is very important for target localization and identification in different acoustical zones of deep water. In order to distinguish the multipath characteristics in deep water, the Northwest Pacific Acoustic Experiment was conducted in 2015. A low-frequency horizontal line array towed at the depth of around 150 m on a receiving ship was used to receive the noise radiated by the source ship. During this experiment, a beating-splitting phenomenon in the direct zone was observed through conventional beamforming of the horizontal line array within the frequency band 160 Hz- 360 Hz. In this paper, this phenomenon is explained based on ray theory. In principle, the received signal in the direct zone of deep water arrives from two general paths including a direct one and bottom bounced one, which vary considerably in arrival angles. The split bearings correspond to the contributions of these two paths. The beating-splitting phenomenon is demonstrated by numerical simulations of the bearing-time records and experimental results, and they are well consistent with each other. Then a near-surface source ranging approach based on the arrival angles of direct path and bottom bounced path in the direct zone is presented as an application of bearing splitting and is verified by experimental results. Finally, the applicability of the proposed ranging approach for an underwater source within several hundred meters in depth in the direct zone is also analyzed and demonstrated by simulations.
基金Supported by the National Natural Science Foundation of China under Grant No 10834009.
文摘Based on the exact solutions for the second-harmonic generations of the fundamental longitudinal and transverse waves propagating normally through a thin elastic layer between two solids, the approximate representations termed as 'nonlinear spring models' relating the stresses and displacements on both sides of the interface are rigorously developed by asymptotic expansions of the wave fields for an elastic layer in the limit of small thickness to wavelength ratio. The applicability for the so-called nonlinear spring models is numerically analyzed by comparison with exact solutions for the second harmonic wave reflections. The present nonlinear spring models lay a theoretical foundation to evaluate the interracial properties by nonlinear acoustic waves.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11474308,11574343,and 11774377)
文摘Ultrasonic inspection of austenitic steel weld is a great challenge due to skewed and distorted beam in such a highly anisotropic and inhomogeneous material. To improve the ultrasonic measurement in this situation, it is essential to have an in-depth understanding of ultrasound characteristics in austenitic steel weld. To meet such a need, in the present study we propose a method which combines the weld model, Dijkstra’s path-finding algorithm and Gaussian beam equivalent point source model to calculate the acoustic fields from ultrasonic phased array in such a weld. With this method, the acoustic field in a steel-austenitic weld-steel three-layered structure for a linear phase array transducer is calculated and the propagation characteristics of ultrasound in weld are studied. The research results show that the method proposed here is capable of calculating the acoustic field in austenitic weld. Additionally, beam steering and focusing can be still realized in the austenitic steel weld and the beam distortion is more severe in the middle of weld than at other positions.
基金Supported by the National Natural Science Foundation of China under Grant Nos 41274134 and 81527901the '12th Five-Year Plan' Period for Informatization Project in Supercomputing Key Demonstration of Chinese Academy of Sciences under Grant No XXH12503-02-02-2(07)
文摘The phase relation of harmonics in high-intensity focused ultrasound is investigated numerically and experimen- tally. The nonlinear Westervelt equation is solved to model nonlinear focused sound field by using the finite difference time domain method. Experimental waveforms are measured by a robust needle hydrophone. Then the relative phase quantity is introduced and obtained by using the zero-phase filter. The results show that the nth harmonic relative phase quantity is approximately (n - 1) π/3 at geometric center and increases along the axial direction. Moreover, the relative phase quantity decreases with the increase of source amplitude. This phase relation gives an explanation of some nonlinear phenomena such as the discrepancy of positive and negative pressure.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40674059 and 10774158.
文摘Theoretical and numerical study on the coupling acoustic field of the plane p-wave to a cased borehole is carried out. The medium outside the cased borehole is modeled as the porous medium. The scattering field characteristics in the cased borehole are investigated when a plane fast p-wave is incident in tilt to the cased borehole from the porous medium. The scattering fields inside and outside the cased borehole are analyzed and deduced by Biot's theory under the boundary conditions on each interface, and they are numerically studied. It is found that the scattering field has strong resonant characteristics and there exists a series of resonant frequencies and peaks. The effects of the frequency, radii of each interface, incident angle, porosity, and other parameters on the resonant acoustic field have been investigated in detail in the fast and slow formations respectively. The resonant characteristics of the scattering field are also analyzed from the physical sense.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11434012,41561144006,and 11125420)
文摘Ocean noise recorded during a typhoon can be used to monitor the typhoon and investigate the mechanism of the wind- generated noise. An analytical expression for the typhoon-generated noise intensity is derived as a function of wind speed. A "bi-peak" structure was observed in an experiment during which typhoon-generated noise was recorded. Wind speed dependence and frequency dependence were also observed in the frequency range of 100 Hz-1000 Hz. The model/data comparison shows that results of the present model of 500 Hz and 1000 Hz are in reasonable agreement with the exper- imental data, and the typhoon-generated noise intensity has a dependence on frequency and a power-law dependence on wind speed.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11434012 and 11174312
文摘The horizontal-longitudinal correlations of the acoustic field in deep water are investigated based on the experi- mental data obtained in the South China Sea. It is shown that the horizontal-longitudinal correlation coefficients in the convergence zone are high, and the correlation length is consistent with the convergence zone width, which depends on the receiver depth and range. The horizontal-longitudinal correlation coefficients in the convergence zone also have a division structure for the deeper receiver. The signals from the second part of the convergence zone are still correlated with the reference signal in the first part. The horizontal-longitudinal correlation coeffi- cients in the shadow zone are lower than that in the convergence zone, and the correlation length in the shadow zone is also much shorter than that in the convergence zone. The numerical simulation results by using the normal modes theory are qualitatively consistent with the experimental results.